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Feb. 27, 1923. i 1,446,650 B. MACPHERSON ELECTRICAL CONDENSER Filed Oct. 22, 1919 2 sheebs-sheet l i mmmmmmmm Feb. 27, 1923. 1,446,650 B. MACPHERSON ELECTRICAL CONDENSER Filed Oct. 22, 1919 2 sheets-sheet 2 Il Il A TTORNE Y Patented Feb. 27. 1923.

UNITED STATES PATENT OFFICE.

BYRON MACPHERSON, OF ROXBURY, MASSACHUSETTS, ASSIGNOB-TO WIEELSS SPECIALTY APPARATUS COMPANY, OF BOSTON,VMASSACHUSETTS, A CORPO- RATION OF NEW YORK.

ELECTRICAL coNnnNsna.

Application lcd October 22. 1919.

To aZZ'wh/o'm 'it 'may` concern:

Be it known that l, BYRON MACPHERSON, a citizen of the United States, and a resident of Roxbury. Massachusetts, have invented certain new and useful Improvements in Electrical Condensers1 ther principles ot which are set fort-h in the followingspecifi'- cation and' accompanying drawings, which disclose the'form of'theinvention which l now consider to be the best of the various forms" in which the'principles' of'the'invention may be embodied. -v l f This invention relates to improvements 1n electrical condensersof "the plate lor sheet type, especially of the type whereinthe condenser ls divided into sections and the sections connected in series foi" highpotential service altho not limited to series condensers, and the invention yconsists of certa-in" improvements iny the' means' for clamping the stack. This application is a continuation in part of my application Serial No.301,498 fleddune 3, 1919.- i

' Condensersas above mentioned are formed by placinga dielectric between two conductors. The conductors may be electrically separate to permit of thecombination functioning as 'a condenseri If a'potential dif'- ference is applied across the two conductors electrical ener'gyqis stored in the dielectric. In ractice condensers are constructed of 'a com ination of dielectrics and conductors. These are arranged in a design that is based on factors which'include the natures of the associated dielectries and conductors, the electric'requirernents of the condenser7 and the space and cost considerations.

Mica is themost desirable solid dielectric for use in a condenser as it possesses certain useful properties such asa high dielectric constant anddielectric strength, mechanical property of being easily split into thin'tilms of approximatel)v constant 4thickness,V and then being easily cut to the required size, its chemically inert nature, low dielectric hys# terises7 high specific resistance and low reaction to small temperature changes.

Full use of these properties is conditional on the degree of intimate Contact between the mica and its associated conductors. Since mica is expensive and space factor is Serial No. 332,479.

generally important, films whose thickness depends on the potential difference towhich the condenser is to 4be subjected are used. The films are madeas thinas possible in keeping with the conditions of the electrical use ofthe condenser.' The'mica is, therefore, operated at the highestsafe'potential difference per mill thickness `of mica. 'Since the' dielectric strength Vper mill' of asolid dielectric increaseswith decreasing thicknessof the dielectric, the useofseries con- `densersis more economical thana condenser of thick dielectric built'as a single section because `higher operating potentialfdiferences per mill thicknessfcfmica canbe obtaime-d'24 utilizingA alv less` amount l of dielectric perunlt of energy 1carrie'dbyithe condenser. f i

' Ifthe mica-pand.' conductors are not infinrtlixnate cor1tact,'tl1at'is"to 'say'if`a second dielectric' in addition to the m'icafisj present .between the 1conductors se'rious'losses'which mayeven' extend to breakdown' occur. This partial vacuumor a'gas; or itmay befaliquid or it may be' a solid.` For'example a loosely built-stack erected finf air contains films 'and Vbubbles of airlbetween theV micas and the conductors.- Both the dielectric constant and theldielectrcistrenhfrth of. air are much lower-than mical Iffthe-condenser is subjected to va potential: 'difference at "its 4terminals that -wouldhave vbeen safe were the' micas and'conduct'ors in-intmate Contact, this potential difference is rio longer safe now that theiairiis 'alsofpre'sent. ln spite of the apparentiincrease` of insulation between the conductors; the condenser -now brushes across the thinlin `ot' ail-j yThis is due tothe electrical relation that theipotential' difference' per unit" distancer across two series Insulators dividesiinthe` inverse ratio of their dielectric constants. :lFor example, if in a three and one half mill space between two conductorssubjected to a potential difference we had 3.0mills of mica and 0.5 mills of air, with mica of'a dielectric constant 6 and air of dielectriccconstant unity, the potentialv difference across the air per mill would be six times the potential difference across the mica per mill, or in the givenease the potential difference 1across the air one halfof the total #applied potential difference. If the applied potential difference were `200() voltsuthe 3.() rnills'of micafwofuljd be To 1000 volts and the 0.5 'mais af air io moo vous. Break down of the air would occur as evidenced by brushing. lf the potential difference were applied for a oreat enough period. the heat developed by this brushing would cause complete break down of' the condenser. Howeveryithe mica wereinintimate `contact Wth-the conductors break down -would not ocm since the dielectric strength of mica ris considerably-greater than 6663; xiofl-ts per slime phenomena lto a lesser degree would-take placein en oil arasite dielectric xvhe're thefmain dielectric 11s mica. Another 'ctor played by theparasitical dielectric comes intb ,playwh'en the condenser is -nsed amically or witli-altei1iating current. llico. has 4a low dielectric'loss. Materials suclnas bakelite and 'condensite'and fbin'ding wal'nlsheshave a high dielectric loss. Should 'thesematerials be nsedtsbinders in building-u'pfla stack'and should they 'remain between the conductors, failure may occur vwhen the condenser =s operated dynamically. 'll-his -.-s due 'to a combination of causes.l na'meLy--high `strain across-the parasitical dielectriean'd resultant abnormal loss in this Ymlalt'erial due to z'both the above mentioned high strain-and high dielectric =loss o the material. illhe=heat developed may cause complete :breakdown of the Econdenser.

Byfmy present invention I have provided a clamp' which can be adj usted to the correct pressure before placing it n-a container or casing -and surrounding it with an insulating seal-such as wax or oil. Thus when the stoxlc is -plaoed in the casi: fr and surrounded with wax or other filler an the cover placed imposition it will be ready for operation and -th'e'i rassure on the stackis maintained ihdepen ently of the casing and cover rhichcan be therefore of any suitable ina- (,erial` 0f required electrical strength chosen independently of its mechanical strength. By my construction it is possible to inspect the stack with the-final pressure applied and correct it for the alinement of the section conductors, the insulators between the sections-and the-section terminals before placing in the casing. Y

It will be seen that the variations 1n the volume V0f the seal within the casing due to expansion or contraction due to tempera- Eture changes of the mass does not elect the 4pressure exerted by the clamp which is independent of the cover. The relatively large expansion coefiicient of oils and waxes that may be used for fillersT over the expansion coeflicient of the case causes an internal pressure on the entire case and cover when the temperature of the mass is raised and, if the case is rigich'the cover must yield and the losses increase rapidly.

My invention is especially applicable to the type of stack in which the two ends are at 'a dill'erence of potential and is embodied preferably as an 'insulating clamp: *that is a clamp in which the two ends of the stack are connected by a member comprising insulatingV material. An advantage of my forni of clamp resides in the fact. that the capacity of the condenser remains constant with time and use.

This clamp in ,particular comprises anetallic end blocks -or members engaging the ends of the stack :md a Yflexible band of insulating material connecting the Vmembers and drawing'the same into clamping' relation against the ends of the stack,-` the ends of the stack being at high potential differences.

Obviously it is possible to place the unit in any desirable casina constructed of any desirable materials.- Tiesematerials would then be only strong enough mechanically to resist physical damage to thecase in handling and do not require mechanical Vdesign strong enough to rtake care of the condenser pressure. I

An -object of this invention is tolproride a clamp which will maintain the insulators or dielectric. and conductors `as above -mentioncd4 in 'intimate contact..

Another object of this invention is topvovide aclamp colnprising insulating niaterial for eondensers comprising foil sheets and insulators of fragile flexible uniteriah eflii-icntly maintaining them iu intimate contact as a imitar).7 structure and properly in sulated.

The invention consists furl-her in details or ronstruotion and combination of parts hereinafter more particularly described and claimed.

In the accompanying drawings which form a part of this specification Figql is a side elevation with parts in section illus trating what I now consider lo he the preferred form of the invention.

Fig. 2 is an end elevation with parts in section of the structure of Eig. 1.

Fig. is an end elevation of a modilied 'forni of the invention. the casin; r boing omitted.

Fig. 4 is a side elevation of the Structure shown in Fig. 3.

Fig. 5 is an end elevation with yparts broken away of another forni of the invention. and

Fig. v6 is a. side elevation o the forni of lig. 5.

leerring to Figs. l and 2 the spare X shown around the stack K and its clamp ll'i llll

1,44e,cso

in the sealing filler or wax protector or casing B is intended to illustrate the wax or other filler casing or coating around the stack for the purpose ot preventing brush discharges and excluding moisture and air. and also preferably around the clamp. This is preferably| a mass of wax cast in protector B as a mold and filling the space X and surrounding clamp A and it may be no more than a thin or surface coat providing that it excludes moisture and air from the interiorof the stack and assists in preventing brush discharges. n the type of condenser on which this invention is an improvement: the condenser consists of a stack of plates or sheets, this stack being adapted for high potential serv ice by being divided into sections which are electrically connected together in series by Various means in accordance with the estab lished practice for many years, and in which any desired manner of connecting these sections in series may Abe adopted, but for purposes of illustration 'I apply the arrangement as shown in Figs. 1 and 2.

The sheets as usual consist of successively located conductors and insulators. In the *present condenser such insulating and oonducting sheets may beof any desired material but I use metal foil (as lead) for the conducting sheets and mica for the insulatinglsheets andrny condenser is therefore known t0 the trade as a mica condenser, or specifically, a high potential mica condenser or as a transmitting condenser 'for use in radio communication.

A desirable feature of construction ot' this kind is a small volume of the apparatus, but the highpotential developed malzes this a different problem. The same is true in respect to exposing a minimum of' the conducting parts which are at high potential Other problems have arisen in connection with the importance of the construction whereby the condenser stack is most desirably held under compression and kept permanently dry and free from air inside of the stack and whereby brush discharges are prevented. i

l have illustrated clamp A Figs. 1 and 2 applied to a series of sections S constitutingl the stack K and connected together by connectors v1 of sheet copper. Each connector at one end 2 is bent around the foil bunch 3 at one end of a section S and soldered at 4 to the outer or remote side ofthe foil bunch 3. The connector 1 then extends between adjacent sections parallel thereto and is bent at its opposite end 5 around the foil bunch 3 at the opposite end of an adjacent section S and soldered to the outer or remoteside thereof as indicated at L1. The inner portions of the connectors 1 are unattached to the foil bunches. Separators 6 are interposed between said adjacent sections S and upon opposite sides olf the con nectors 1 for insulating purposes.

This stack construction is more fullyv illustrated described and claimed in the above mentioned co-pending application Serial Number 301,498 and is illustrated here merely to show an application of the present invention.

The stack K is mounted upon a metal clamping or base plate 7 which is also delined as a pressure member. lnterposed between the clamping plate 7 and the stack l( is an insulating sheet 8.

Upon opposite sides of the stack are pairs of openings 9 in the clampingplate; the lower portion of these openings heilig coni cal to receive the head 10 of screws 11. Clamping bars or rods 12 provided with threaded openings 13 adjacent. to their ends receive the threaded portions ot the screws 11. These clamping bars are arranged parallel to each bther 'upon opposite sides of thc stack. Insulatingmeansis preferably provided for connecting the two ends of the stack which areigenerally at high potential differences. Preferably a'band or loop 14 is therefore attached at one end to'o'ne clamping rod'12, extendsover the opposite end o'the stack and over a brass convex pressure member or bloclcl on 'said end and is attached at its other end to the other clainping'rod 12. The'pressure'blocksl is insulated from the stack by a sheet ot' liber 16 and prevents the loop 14 from damaging the mica and foils constituting the stack. Furthermore the clamping rods 12 are spaced froml the lstack sutliciently to keep the band 14 out of contact with the sides of the'staclr. Theba'nd 14 preferably' consists of a strip of flexible insulating material of high tensile strength and practically non stretchable. The band is formed by looping the strip and 4securing the several plies 1T by means of eyelets 18. Therlosed ends 1%) extend around Vor below the clamping bars 12 forming a dependable means of securing the band thereto. This arrangement provides a doubled intermediate portion extend ing from one clamping rod over the' top or around the opposite end of the stack and pressure member 15 to the other clamping rod and comprising the parts 2O and Q1. each having several plies 17. .i

When' band 14 is in 'pla/ce around the clamping rods 12 and the end of the stach, the screws 11 are adjusted drawing the base plate or lower pressure member and the upper pressure member towards each other whereby the pressure exerted by clamp A upon the ends of the stack is adjusted to the proper amount. The adjusting screws 11 are located at opposite sides of the stack and the adjusting force is appliediat both sides of loop 14 whereby th(` pressure is transmitted evenly to the ends of the stach without danger of `tiltin,"r or dislooutinpr the elements thereof.

The (1l-amp maintains pressure .upon `the stack at lall times ,whereby the insulating sheets and conductors ot' each section 4and the several :sections are inutntainecl in intimate Contact.

In assembling the steek is 1,)reheated and the screws 1l are-tightened )while the stack is under pressure. All this willfbe done before placingthe ,unit in the casing and 4securingit thereto thusnllowing inspection of the stack before being mirrounded by -wax or other filler.

Theband ispreferaibly eoinposed of fish paper altho canvas or other fiberous insulating material may'be fused. The material composing the hund vis capable of Standing up under hot wax and does not increasein length appreciably under tension. The oonstmction herein described i@an :be easily assembled and iprovidesa, highdegree of eficiency at a :minimum oost. g

An'importunt feature of the above wnstruction resides vin :the location ofV the drawing liars or clamping rods t2 Well outside of the voltage gradient line and Ves the fiher is a ine nomoonduetor this is ideal m od .of construction 4in eyeing;-v may.

course, the stack K of-this condenser, like any condenserzstack of 1sheets;requires initial treatment -duning manufacture .for the purpose of rernofmgl internal airiand moisture, and consolidating the stack :of sheets before .being covered withthe .coating of wax which thereafter isto 4keep .out the air and moisture. Any of the various-well known methods may ,be used for this vtreatment which usuallyT include `immersion `.in molten wax. in or out of vacuo. and a eompression or variation of the conipressio'n of the stack. For .the latter purpose :a .clamp is used during the process hut vin this in stance the clamp A, that is the stackl( and its clamp A may :1ct as a unit during the treatment. The stack and clamp inithe present ease are assumed to have heen .properlxf treated as above and in proper vcoificli-tion of clamping pressure and are read-y tovbe inserted in easing B and surrounded by .wax Xor other filler.

The wax protertor P is so called because it may serve initiallyos aimold for the :wax easing X whenthe latter fills-container B vet thereafter B reinainsas a permanent'. part ofthe assembly for the purposeof pro- Lenting the wax filler which it does VWhether the filler be merely a coating around the stack or a thick mass filling protector-B.

ln preparation for=thecastingiof the wax in receptacle B the stack K and .clamp A in place around it are inserted in protector B as the -mold und protector. If desired indeed the receptacle B may be used previously for the above treatment ofthe stack,

i/ewso i. e.. all4 hree parts, stuck'l clamp A, und receptacle .ll may .he 'uSQfl l/,Oglfther in the preliminary treatment of the stack.

The .wax is then cast ,in lthe .mold B round the stack and clamp, theletter be? ing supported :bynd secured ,to the easing thru the base plate 7 which is secured tothe easing in any suitnlile ,manner inde endently of the .wan duringoolinganda r ithas solidified. i e

Before the wax is ,appliedpne end Aof the lowest .seetion..S is nonnecoed by lead .2.2 to the casing B. The lead; is preferably soldered tothe .climpingiplatef thecasing B yconstituting ,the low potential teminal LPT. .The .Steek K isfealeedqby .the easing ll provided with 0011er C having' an opening 23 with ariupper reeess 24. A terminal .Stad ,therethmr copstitutes the high potential terminal HP 4T. A lead Qloonneots oneend of thetopsection Sthereioes mOi-.8 fully dbed@ .here- -nater. flfhe expressions fhigh .potential terminal .and Flow potential terminal are of course only :relative .terms iand the aotual high 4potenti-al and 10Wy ,potential depends entirely on theronditionpf rthe circuit in whiehvlthe ycondenser .maybe At the-time when ,the s taokandlamp are vcast in wax thehigh potential-lead 25 ,is leftprojecting-:abqo the Waxjn prepamtion for the appleaiion ofthecondenserover.

Ater the v ifax if .used .,injB Chas been cooled und solidified .the top innover may he applied upon ,gasket Ginterposed for wziterlightness. Before ,the `cover, is :Igpplied the :high potential` leadrz Aleft projecting abovethe wax isiconnected up it gasket G nmlnrith .terminal H I T; The menus for making suoli connection arefdesignedy to .ohyiate the ,necessity of a long.r lead. The terminal studuH P T .extends :thru opening 23 in the lcover, is `provided .with a head 26 at itsnlowerend to which the lead -25 is solderedlaud is threaded at its upper end. A .brass knurled insert-27 surrounds-the upperl portion .of ,the stud and Afits .in the reess 24 ontbe top of the cover. A. threaded lock washer 28 is`,now placed on ;the tlireadedstud. drawing Ythe head 26 up against ,the bottom of lthe `cover. A rasherBQ is placed. above 4.this and@ nut 30 is ,provided for .clamping lany desired .connection to terminal The cover is non' .placed in .position Aand secured to 4the casing ,iw suitahle.fasteningdevices such as serensC". After the .cover ,issecured in ,position the. spa-,hetween ;the cover Iand 4wander other filleialre :1dy in thecnse is filled -with wax ,or other ,filler thru a suitable opening 431 in the cmertxyhich is Ithen closed ,with a ber screw o r plug 32 making the casing air tightnd protectinolleed 25.

The particular condenser here siiounjhas a capacity of 0.0051 micro-.forati in lertensire use for transmitters and radio communication. In the example disclosed each section S may consist of the size, number and thickness of sheets which will give it a capacity as above mentioned.

The wax protector or casing B may be o any desired material or shape because it has no necessary mechanical or electrical co-operation with the condenser stack and the specific embodiment of clamp herein disclosed. Thus it may consists of any simple wood or fiber box of any size, or shape if desired. In fact as the stack l and clamp A constitute a complete operative condenser they may be used without any covering over the casting or coating of wax, but, of course, it is extremely advantageous to provide a wax protector and to also have it of metal as the most practical form of protector during use of the condenser.

I prefer .that the casing B be of metal such as aluminum molded thin to shape as a singleand economic construction. Aluminum is light, relatively cheap and easily molded but any other material may be used such as a tin or sheet brass casing.

The walls of the container B are substantially .vertical and'farranged close to the lower portions ofthev clamp. The band 14 being of fibrous insulating material of substantial width, insulates, in addition to the wax, or other iillerthe adjacent portions of the stack from the adjacent walls of the casing, preventing brushing.

n the construction herein disclosed the clamping means is entirely distinct from the cover and independent thereof; the latter playing no part in compressing the stack. The cover may consist of any suitable insulating material such as electrose7 or the like, molded as shown;

Referrin to Figs. 3 and 4 I have illustrated anot er form of the invention which may be used either with or without a casing as above described. In the construction shown in Figs. 3 and 4 the sections S' are arranged in superimposed position and connected in series in any suitable way altho I have illustratedthem 'connected as in Figs. 1 and2.

At the opposite/'ends of the stack are placed metal blocksor pressure members 34 each separated from itsend of the stack by means of a fibrous sheet 34. The outer portion of each block is provided with a pair of transversely Vextending spaced grooves 35 having convex bottoms 36 as shown in Fig. 3. Extending around the stack and blocks are strong iiexible fiber bands 37 of any suitablel material, referably cord, having good insulating qua ities. The portions of the bands extending over the'blocks are located in the grooves 35 which prevent .displacement of the bands and hold them in osition. The pressure blocks provide a firm n utment Acontact of the elements thereof.

`tion of 5 and 6 may for the bands and prevent them from damaging the elements of the stack which are built up as described in connectionV with Figs. l and 2. Upon opposite sides of the stack the bands 37 which are spaced are con nected and drawn together by means ol transverse' toggle fastenings 38 of like material. These fasteninvs 38 draw the lateral portions of the bands inwardly toward each other thereby drawing the blocks 34 toward each other clamping the blocks against thil ends of t-he stack and providing intimate The fastenin s 38 are at opposite sides of the stack and t e pressure exerted on the blocks or pressure members is uniformly distributed over the ends of the stack when the bands are drawn up thereby preventing tilting or distortion of the stack.

The opposite ends of the stack are preferably at different potentials and the construction of Figs. 3 and 4 provides a clamp which properly insulates the ends of the stack from each other and at the saine time clamps thc elements thereof into intimate contact, mailitaining the condenser at a constant capacity.

Thestack and clamp may be placed in a casing and treated as above described.

The condenser as above described and illustrated in Figs. 3 and 4 has been tested and found successful for transmitting condensers operating at 21,000 volts and carryinn` 18 amperes.

in Figs. 5 and e is disclosed a modification in which the use of a clamping plateA describedA in connection with Figs. 1 and 2 is obviated, the clamping rods being secured directly to the bottom of the casing which constitutes a pressure member. Reerrin to Figs. 5 'and 6` the casing Bzis provide with threaded openings 39 u n opposite sides Aol the stack K2 resting thereon. Threaded in these openings are screws 40 having heads 41 at their upper ends. Clamping rods 42 are slidably mounted upon thescrews 40 between the heads and the casing and form means forsec'uring the band or loop 43 having the construction shown in Figs. 1 and 2 and as above described.

- This band extends overa covex pressure plate 44 on top ofthe stack K. substantially as shown. With the exception of the means for mounting the'clamping rods 42 the construction is the samev asin Figs. 1 and 2. Upon the .adjustment of screws 40 the band exerts a uniform pressure overthe ends of the stack and resses the stack firmly against the bottom o? the casing and the elements thereof in intimate contact. The construcalso'be treated as above described andA surrounded by wax or other filler.

It is toibe understood that the invention 1s not limited to the embodiments andfeatures specifically shown and described herein, but

such embodiments and, features are subject to change and modifications Without any departure from the spirit of the invention.

I claim:

1. In an electrical condenser, a stack comprising sections connected in series and haw ing its ends at a.A difference of potential, pressure members onthe opposite ends of tbe stack and a flexible binding device of insulating material connecting said members for clamping the elements of the stack together. Y

2, In a electrical condenser., a stack baving its ends at a difference of potentialz a clamp compressing said stack and including inea-ns insulating the ends from each otier, and a metal casing enclosing said stack and clamp, said casing being at the potential of one end of the stack.

3i.. In an. electrical condenser, a' stackA of `sections connected in Series and com rising alternate sheetsof conductorsand die ectric. said Stack having its ends at adiference of potential, a clamp compressing said stack to bring said sheets into intimate Contact and comprising -means insulating said; ends from each. other, a, casing ofmetal enclosing saidlstack and clamp andl at the* potental oi one end.- ofthe stack, said clamp functioning independently oi said casing, and a filler of insulating material embedding said clamp and stack within the' casing.

`4. In an electrical condenser, a stack and a clamp compressing-said stack and comprising a pressure plateon one end of the stack and an insulating member having lateral 'portions secured to said plate and arranged along oppositefsidesoi the stack and an intermediate portion extending around the opposite end of the stack.

5-. lin an electrical condenser, a stack of alternately arranged: conductors and dielectric and.l a'clamp compressing said stackand comprising: pressure members upon the ends of the stackand a band of flexible insulating material connecting saidf members to compress the' stack;

6, n. electrical condenser comprising-` :i 'stack-21. plate engaging one endo'thefstaelr. clamping bars adljustably connected to said Y plate and arranged upon| opposite sides of said stacin'apnessurefmember at the other end! of saidl Stacie andra flexibleV band of insulating material extendingaround. said pressure members and; connected tosaid bars, whereby the elements of said stack maybe maintained? in intimate contact.

71. 'AmI electrical condenser comprising a casing a c ondeznierl stackwithin said casing and'` comprising alternatelyarranged conductors and insulators, a pressure memberupon: one' ond o said stack, clamping bars adjustably connected within said casing upon4 oppositie-sides ofi saidfstack, and af loop innesco of flexible insulating material having closed ends connected to said bars :1nd extending from one of said bars to the other around said pressure member und at opposite sides of said stack, and a filler in said casing in which said stack and clamp are imbedded.

S. 1n an electrical condenser, a stack comprising sections connected in series, composed of alternate sheets of foil and dielectric and having its ends at a dilerence of potential, a clamp comprising preurc plates at opposite ends of the stackand in cluding means insulating,T the opposite'ends of the stack from cach other, a metal casing in which the clamp and stack rest, said casing,lr constituting one terminal of the stack, said clamp being independent of the casing, an insulating cover for said casing, aterininal connected to the stack and projecting through said cover, and an insulating filler' in said casing surrounding said stack: and clamp. 4

9. In an electrical condenser, a Stack, pressure plates on opposite ends'o the stack. pressure-applying means engaging one4 ressurc plate and a connection of flexible: 1nsulating material for transmitting apressure. to the opposite pressure plate from said pressure-applying means,A whereby the stack is compressed between said plates.`

10. 1n an electrical condenser, a stack comprising alternate sheets of foil and d'1- elcctric, pressure plates upon opposite ends of the stack and means for causing said pressure plates to. compress the stack and including several' plies of flexible insulating stri il). In an electrical condenser, a. stack coli-uprising sheets of conductors and dielectries` pressure plates upon opposite ends of the stack. a flexible connection comprising several plies of insulating strip and having! a portion extending1r around one pressure plate and at opposite sides of the stack and means interposed between the other plate and the connection tor exerting alongitudinal stress thereon at opposite sidesto. clamp said plates against the stack.

12. 1n an electrical condenser, a. stack comprising sections connected in series and composed of alternate sheets of foilund dielectric, pressure pla-tes upon opposite ends of the stack, means for clamping said pressure plates against the stack comprising a flexible strip of insulating materiel arranged' in plies and connect-ing the plates` a metal casingr receiving said stack and clamp. terminal leads from said stack and a filler of insulating materiali Within the casing surround-ing the stack'.

13. An electrical condenser comprising a stack, a pressure member bearingr against one end of the stack, and a clamping member looped over theV other endf Of the stack and having two ends adjustably secured to the pressure member at the rst end of the stack, whereby the stack is clamped between the pressure member and the looped end of the clamping member.

14. In an electrical condenser, the combinntion with the stack, of a metal casing enclosing the stack, a metal pressure member in the metal casing and between the easing and the stack; a yieldable clamping 10 member, and means co-operating with the pressure 4member to vary the pressure exerted by the yielding clamping member on the stack.

B. MACPHERSON. 

